Trap switch



A. W. F RUH TRAP SWITCH Filed May ll, 1950 Aug. 19, 1952 f m W.m

u n Il WM Patented Aug. 19, 1952 UNITED STATES PATENT OFFICE 4 laims.

-The invention relates generally to switch* mechanisms, and more particularly to a so-called trap switch for use in burglar alarm-systems, or the like.

Trap switchesof the type here involved, in the past have generally comprised a'stationary contact adapted to be housed in a suitable case or housing which ispi'ovided with means for attaching the switch to a wall, or other surface. The'casing is provided. with an opening in a side' wall thereof adjacent the stationary contact, the opening being of a size to receive a relatively movable contact to permit engagement of the later with the stationary contact, such contacts being constructed to frictionally engage one another, whereby they are normally maintained in engaged relation. The movable contact is connected to the free end of a flexible conductor, with the opposite end of the conductor being securedl to a terminal enclosed in a suitable casing or housing, and adapted to be.mounted on a secondsurface or object. In use, the switch mechanism above described is inserted in series with a burglar alarm system ofthe normally closed type, wherein the opening of the circuit at any point will actuate a relay and burglar alarm. Trap switches of this type are particularly useful in applications such as across open doorways, or across storage racks, shelves, or

the like, in which case the exible conductorv would be stretched across the doorway or shelf opening. When stretched across Aa doorway, it is not readly seen, and an intruder thus may strike or kick the cord, withdrawing the movable contact from the stationaryk contact, and thus actuate the alarm. Likewise, when employedin connection with shelving, etc., the conductor may be stretched across the shelf openingwso that articles cannot be withdrawn fromV the shelf without removing or vcutting thecord ex.

tending thereacross, again actuating thefalarm.

Switches of this type are oftentimesfexnployedn.

in connection with alarm systems-oi the central station type, wherein actuation of the alarm system also actuates an indicator inal central .A

alarm station, such as those operated by various protective associations, n

When incorporated in `a central lalarni system, the tra-p switch, as well as the other switches in the local burglarsystem, areprovided with additional `switch contacts for'the closing of the central alarm indicator, and due to4 the parti.

. 2 Y ing of the --central alarm circuits. is par; ticularly true'in the case of trap switches, as the frictional connection between the station` ary and movable contact is such that a relatively large lmovement of the movable contact i`s're`' quiredV before the circuit is actually broken.

The present invention, therefore, has among its objects the production of a trap rswitch for use in burglar alarm systems, such as" that de scribed, wherein the local alarm system is actu'- ated prior to the actuation of the central system, and prior to the separation of the frictionallyr engaged contacts. n

Another object of the invention is the pro'- duction of such a trap switch, having the above advantages, which is very simple in construction, relatively inexpensive to manufacturaand positive in action.

A further object of the invention is thepro duction of su'cha trap switch which is provided with a pair of contacts in series with the main contacts of the switch, and adapted t'o be actu-"- ated prior to Vseparation of the main contacts.

Many otherv objects and advantages of the construction herein shown and described will be obvious to those skilled in the art from the disclosure herein given.

To this end my invention consists in the novel construction, arrangement, and combination of `part'sherein shown and described, and more lpar-'- way, or the like, illustrating the mounting of a trap switch therein;

Fig. 2 isa longitudinal,l sectional view through.

the movable contact structure employed;

Fig. 3 is a sectional view through a trap switch embodying the present invention taken approxi imately on the line 3-3 of Fig. 4;

Fig. 4 is a side'elev'ational view of the switch structure illustrated yin Fig. 3, with the cover'l or housing, shown .in section, andthe movable tconttact in'engageinent with the stationary con# Fig. 5 is a view similar to Fig. 4, -with the movable contact removed, and illustrating the positions of the other switch elements; and

Fig. 6 is a transverse sectional view taken approximately on the line 646 of Fig. 3.

Referring to Figs. l and 2, I indicates generally' a housing enclosing the switch mechanism,

including the riativeiy stationary contact mounted, for example, on a wall surface -2 forining a portion of a hall or doorway. Mounted on the opposite wall 3 is a juncture box 4, and operatively connected thereto at one end is a flexible conductor the opposite end of which is connected to a movable contact structure, indicated generally by the numeral S. The latter may be engaged with the stationary contact positioned in the housing I, and operatively connected in series into the burglar alarm system by conductors 1 and 8. Thus, if' the conductor cord is struck by a leg, or other object, the movable contact member 8 will disengage the stationary contact and be withdrawn from# the housing I, thereby actuating the alarm.

The movable contact structure G, is of the usual construction and comprises a tubular sleeve II, closed at each end by respective plugs I2 and,V Secured tothe I3 threaded into the sleeve II. plug I2 and extending outwardly therefrom is a shank I4 terminating at y its free end in a ballshaped contact i5, the shank I4 being threaded into the block I2, and locked in position by a nut I6 and lock washer I1. The free c nd I8 of the conductor 5 is secured to the shank I4 by washer I9 and lock nut 2|, the cord 5 extending through a bore 22 inthe block I3., Positioned in the sleeve II andk encircling the cord 5 is a washer 23 and expansion spring 24, the latter seatingcat one end on the block I3, and at the opposite end on the washer 23, with the lastmentioned end of the'spring having coils of reduced diameter to` provide eiective engagement between spring and washer 23. The conductor 5 is knotted, as indicated at 25,V against which the washer 23 bears. In installing the device, as illustrated in Fig. l, the conductor 5 is made of a length to place vthe springv 24 under compression when the movable contact kl5 is engagedwith its cooperable, stationary contact, so that-the cord 5 is maintained taut at all times.

The terminal box 4 is of standard construction, andpmerely provides means for connecting the adjacent end of the conductor 5 to the conductor 8 in the alarm system, at thesame time firmly anchoring such end of the conductor; ,consequently, the `detailsof such juncture box form` no part of the present invention.

Referring to Figs. 3 to 6, inclusive, the'relatively stationary contact structure includes a base member 2B, illustrated as formed offan electrically non-conducting material, on which is mounted a stationary contact 21, the` latter, in the embodiment of the invention illustrated, being generallyy U-shaped in cross section, and having a base-portionA 28 through which a mounting screw 29 extends, the latterbeing provided with a cooperable Ynut 3Ithereby rmly attaching the contact 21 to the base member. 26. YExtending outwardly from the baseportion 28 is a pair of oppositely disposed contacty arms 32, the vertical edge portions of the arms being bentinwardly slightly, asindicatedat 33, to formeguid'- ing vmeans for the insertionof the .contact AI5 between `the two arms' 32. VEach of the latter isprovided with an opening 34 therein, the openings being aligned and adapted to receive portions ofthe ball-shaped contact :I5 when the latter is inserted between the two contact arms, as illustrated in Fig/l. The openings 34 thus form detents tending to retain lthe movable contact in engaged position, and the contact 21 is constructed of a relatively resilient material whereby it is necessary to slightlyspring the two contact arms when inserting the contact I5 therebetween. f

Positioned adjacent an open side of the contact 21 is a switch assembly, indicated generally by the numeral 35, illustrated in the present embodiment of the invention as of the leaf type and comprising relatively stationary contact leaves 36 and 31 between which is positioned a movable resilient contact leaf 33. The leaves 36, 31 and 38 are mounted on a series oi insulating blocks 39, 4I and 42 secured in position by screws 43 and '44 extending through the base member 26, respective blocks 39, 4I and 42, and leaves 35i, 31 and 38, each screw being encircled by an insulating sleeve 45, and threaded on the end of each screw are nuts 46 and 4i, respecclamped between the respective blocks and leaves c is a pair of terminal strips, the terminal strip 'being in electrical contact with the leaf 33, and the terminal 49 being in contact with the leaf 4I, providing means for connecting conductors 5I and 52 to the respective contact leaves. Carried by the leaves 33 and 38 are respective cooperable contacts 53 and 54, and the free end of the leaf 31= is bent downwardly toprovide a contact portion 56 adapted to engage the leaf 38 when in the position illustrated in Fig. 5.

The free end of the movable leaf 38 is provided with extension 51 of a'width to be positioned between vthe contact arms 32 of the stationary Contact 21, the portion I51 being enclosed in a sleeve 5B of electrical insulating material. As illustrated in Fig. 4, engagement of the movable contact I5 with the stationary contact 21 will result in engagement of the contact I5 with theextension of the movable leaf 38, movingy the latter downward, and bringing the contacts 53 and 54 into engagement. When the contact I5 is withdrawn from the stationary contact 21, the inherent resiliency of the leaf 33 will cause the latter to assume the position illustrated in Fig. 5, thereby engaging the contact portion V56 of the leaf 31. As illustrated in Fig. 3, the conductor 5I is secured at one end to the terminal 48, and thus to the leaf 36, and contact 53 is connected at its opposite end to the stationary contact 21 by means of a terminal strip 59 interposed between the base portion 28 and the base member 26. one end to the terminal strip 49, is connected at its opposite end to a terminal strip El, and

with the bolt B2, nut 63, and washer B4 provides terminal means to which the conductor 1 of-y the alarm circuit may be connected, the opposite` side of the alarm system, of course, being connected to the movable contact I5. As previously described, the contact leafy 31 may be operatively connected to the central-alarm circuits by means of a conductor 1' secured to the screw 44 by means of a'lock-n'ut 55 and washer 66.

The stationaryv contact'21 and switch mechanism 35 arey enclosed by the housing I, which is provided vwithan opening 61 opposite the.' stationary contact 21, of a size to permit ready entry of the movable contact I5 through theside wall of the housing' and engagement with the contact 21, as clearly illustrated in Fig. 4. In the embodiment of the invention illustrated, the housing I is secured to the base member 26 :by a bracket 68 having a pair of spaced, substantially parallel leg portions 69'connected by an intermediate base portion 1I, the latter being seat-,- ed upon the' base 26 and secured thereto by any suitable means, as for example,- rivets 12 passing through the portion 1I and base 26, The leg pore;l

Likewise, the conductor 52, connected at.

tions 68 are. each -providedwith 'anopening 13 therein, Aeach adapted to receive an inwardly extending projection orqbead 1 4- formed intheadjacent side walls ofthe housingA I whereby the latter is frictionally held rsecurelyiin position on the basejmember '26. Extending across the openfaccioff theA base member 2,6 ijsga sheet of insulatingfmaterial15 held in place byiscrews 16 passing through the base member 26, and nuts 11. As illustrated in Fig. 3, the screws 16 may be positloned at diagonally opposite corners, with the holes 18 in the other diagonally opposite corners providing means for the reception of screws, or the like, for mounting the device to a wall, or other supporting structure.

In the operation of the device, the alarm circuit conductors 1 and 8 are connected by the conductor 5, contact l5, contact 21, conductor 5I, contacts 53 and 54, and conductor 52, so that both the contacts 53 and 54 and contacts I5 and 21 are in series in a circuit. As the contact I5 is withdrawn from the stationary contact 21, outward movement of the contact I5 will permit the movable leaf 38 to move away from the leal.' 31 until contacts 53 and 54 separate, this action taking place prior to complete withdrawal of the contacts I5 and separation of the latter with the contact 21. However, upon complete withdrawal of the contact I5, the leaf 38 will move outwardly into engagement with the contact portion 36 of the leaf 31. The central alarm circuit would be connected in series between the leaves 31 and 38, so that upon engagement of the leaf 38 with the portion 56 of the leaf 31, such alarm circuit would be closed to actuate indicating mechanism associated therewith. It will be apparent that, as the contacts 53 and 54 are positioned to open upon relatively slight outward movement of the movable contact I5, the local alarm circuit is immediately actuated, with a delay taking place between actuation of the local alarm circuit and actuation of the central alarm circuit resulting from engagement of the leaves 31 and 38, as the latter circuit will not be closed until the movable contact I5 has been completely withdrawn from the stationary contact 21. Obviously, if the series arrangement disclosed Awas not employed in the local alarm circuit, it would be diilicult to provide the desired delay between the opening of the local alarm circuit and consequent closing of the central alarm circuit.

It will be noted from the above description that I have provided a very simple but efficient trap switch mechanism which provides a desired delay between the actuation of a central alarm circuit following actuation of the local alarm circuit, which trap switch mechanism is simple and durable in construction, very eiiicient in operation, and inexpensive to manufacture.

Having thus described my invention, it is obvious that various immaterial modifications may be made in the same without departing from the spirit of my invention; hence, I do not wish to be understood as limiting myself to the exact form, construction, arrangement, and combination of parts herein shown and described or uses mentloned.

What I claim as new and desire to secure by Letters Patent is:

1. In a trap switch for burglar alarms, the combination of a generally U-shaped stationary contact, a substantially ball shaped movable contact adapted to be positioned between and frictionally engage the leg portions of said stationary contact, a leaf type switch mechanism inciudingfazreianveiy stationary leaf andra resuient movable leaf, a second pair go't coopera'bl'ef movable contact when the latter is engaged with its cooperable stationary contact operative to normally maintain the second pair of contacts closed. and a third contact leaf related to and adapted to be sequentially engaged by said second movable contact leaf upon the first movable contact being disengaged from its cooperable stationary contact.

2. In a trap switch for burglar alarms, the combination of a generally U-shaped stationary contact, a substantially ball shaped movable contact adapted to be positioned between and frictionally engage the leg portions of said stationary contact, a second pair of contacts one of which is movable towards and away from the other contact, means operatively related to said last mentioned movable contact extending between the leg portions of said iirst mentioned stationary contact and engageable with said rst mentioned movable contact when the latter is engaged with its cooperable stationary contact operative to normally maintain the second pair of contacts closed, said first mentioned contacts being electrically connected in series with said second mentioned contacts, and a third contact operatively related to and adapted to be sequentially engaged by said second movable contact when the rst movable contact is disengaged from its cooperable stationary contact.

3. In a trap switch for burglar alarms, the combination of an insulating base plate, a housing for enclosing said base plate, a generally U-shaped stationary contact mounted on said base plate, said housing having an opening therein disposed opposite said U-shaped stationary contact, a substantially ball-shaped movable contact adapted to be inserted through the opening in said housing and to be positioned between and frictionally engaged by the leg portions of said U-shaped stationary contact, and a leaf type switch mechanism mounted on said base plate and enclosed within said housing, said switch mechanism including a pair of relatively stationary electrically conductive leaves and a resilient movable electrically conductive leaf, said stationary leaves being disposed on opposite sides of said resilient movable leaf with said resilient movable leaf extending between the leg portions of said iirst-mentioned stationary contact and engageable by said first-mentioned movable contact upon the latter being inserted into co-operative engagement with said stationary contact, and said resilient movable leaf serving to establish a closed electrical path through one of said stationary leaves upon said movable and stationary contacts being engaged and to sequentially break the same and establish a second closed electrical path through the remaining stationary leaf upon said movable contact being disengaged from said stationary contact.

4. The combination set forth in claim 3 further characterized by conductive means electrically interconnecting said stationary contact and one of said stationary leaves in electrical series relation, a iirst terminal post mounted on said base plate and electrically connected to the remaining one of said stationary leaves, and a second terminal post mounted on said base plate and electrically connected to said resilient movable 7 leaf, the entire assemblage being enclosed'wthin said housing. .Y 1 Number s ARTHUR W. FRUH. l v2,914,474

n v v REFERENCES CITED 5 VThe following referenpes are of record in the Number le of this patent:

UNITED STATES PATENTS Name Date- Hopkiris Sept. 17,k 1935 FOREIGN PATENTS Country Dat'e I Great Britain July 21, 1927 Italy Oct. 21, 1942' 

